Order Analysis- How can I identify what departments/divisions and products have been ordered within an order?

This is where the s.products variable and merchandising eVars come into play.

https://experienceleague.adobe.com/docs/analytics/implementation/vars/page-vars/products.html?lang=en

https://experienceleague.adobe.com/docs/analytics/components/dimensions/evar-merchandising.html?lang=en

Think of "products" as a special "list of lists" type of value... each product being purchased as a product identifier, it has a quantity of items, it has a price.. but for each product you can stitch in custom events and merchandising eVars per product.

The eVars/events for product A only apply to product A, the eVars/events for product B only apply to product B, etc.

Now, in the documentation, you will see that there is a column for "category" and that some places consider this to be "deprecated"... well yes and no...

It does still have a value.. like maybe you want to track both "cart" and "purchases"... using the category here to separate out the particular usage is valid (and you can also correspond this with appropriate events - there are many ways to go about this).

However, in what you are trying to do, most people will set up a merchandising eVar to hold a SKU, then they will use classifications to apply department / divisions / categorization to the items. This allows you to make changes in past data, since Classifications are essentially processing rules that are done after the fact on the recorded data... 

https://experienceleague.adobe.com/docs/analytics/components/classifications/c-classifications.html?lang=en

Hope this helps.